Generally, superconducting wire includes a metal substrate, a superconducting layer, and a buffer layer for minimizing the difference in material properties between the metal substrate and the superconducting layer.
Such superconducting wire must be used together with a stabilizing material made of metal because it is difficult to pass a high current of 1000 A or more through superconducting wire and the metal substrate cannot be used as a stabilizing material due to the buffer layer. Therefore, in order to conduct a large current, several superconducting wires are assembled and then used, and a metal stabilizing material is generally placed therearound.
Generally, in order to assemble the superconducting wires, they are connected in parallel to each other by soldering. The assembled superconducting wires are joined with a metal stabilizing material through soldering. That is, both the assembling of the superconducting wires and the joining of the assembled superconducting wires with the metal stabilizing material are realized through soldering.
In the assembling of the superconducting wires and the joining of the assembled superconducting wires with the metal stabilizing material through soldering, since the resistance between the superconducting wires is relatively high, the inconvenience in a permanent current operation, which is an original function of a semiconductor, results. Further, since the entire resistance of the assembled semiconducting wires is not uniform, for example, their soldered portions are detached therefrom, current excessively flows in one direction, so that the temperature in the superconducting wires is increased, thereby causing a breakdown of the superconducting state.
In order to solve the above problems, various technologies for joining superconducting wires have been disclosed. For example, Korean Patent Registration No. 10-0360292 discloses a technology of longitudinally connecting superconducting wires, Korean Patent Registration No. 10-0392511 discloses a technology of electrically plating superconducting wires with a metal stabilizing material, Korean Patent Registration Nos. 10-0380630 and 10-0394229 disclose technologies for improving the junction between filaments of multi-core superconducting wires, Korean Patent Registration No. 10-0201752 discloses a technology of manufacturing a multi-core superconducting wire by extruding a bullet composed of superconducting powder and stabilizing material and then coating the bullet with a stabilizing material, and Korean Unexamined Patent Application Publication No. 10-2005-0010228 discloses a technology of joining superconducting wires to normal conductive parts in order to reduce the resistance of the normal conductive parts in a superconducting system.
That is, the above conventional technologies include a technology of longitudinally connecting superconducting wires, a technology of electrically plating superconducting wires with a metal stabilizing material, a technology of performing the junction between filaments of multi-core superconducting wires, a technology of coating a bullet-shaped superconducting wire with a stabilizing material, and a technology of reducing the resistance of normal conductive parts through soldering.
However, the above conventional technologies are problematic in that they require a lot of time and high production cost, and in that, when a superconducting wire coated with a metal stabilizing material is connected to another superconducting wire or an electric connector, soldering must be further performed, so that the heat generated through the soldering influences the previously soldered parts, with the result that the previously soldered parts are separated from the super conducting wire and thus the critical current of a superconducting layer is decreased, thereby incurring the inconvenience in a permanent current operation.
Further, there is a problem in that conventional superconducting wires having square sections cannot be easily joined and wound.